refactor(orchestrator): move run_docker to a lean top-level docker_cmd (#352)

Review feedback: don't bury a parallel docker util in the orchestrator.
But reusing backend.docker.util (docker_mod) isn't right either — importing
it runs backend/__init__.py, which eagerly loads all three backends
(docker + firecracker + macos) plus the manifest/egress/git-gate/supervise
framework (~76 modules), so every orchestrator import would drag the whole
backend layer in.

Compromise: promote the helper to a top-level, framework-free
bot_bottle/docker_cmd.py (single stdlib import), a proper shared home the
orchestrator's docker components use now and backend.docker.util can adopt
later. Verified `import bot_bottle.orchestrator` stays lean (12 modules, no
firecracker/macos backends).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/orchestrator/docker_broker.py

@@ -15,8 +15,8 @@ from __future__ import annotations
 
 import subprocess
 
+from ..docker_cmd import run_docker
 from .broker import LaunchBroker, LaunchRequest
-from .dockerutil import run_docker
 
 CONTAINER_PREFIX = "bot-bottle-orch-"
 BOTTLE_ID_LABEL = "bot-bottle-bottle-id"